Directions

Crust: Whisk flour and cocoa in a small bowl to blend. In a large bowl, beat butter, confectioners' sugar, egg yolk and vanilla with mixer on medium speed, scraping down sides of bowl as needed, 1 to 2 minutes until fluffy. On low speed, add flour mixture. Beat 1 minute or until moist clumps form. Scatter over bottom of prepared pan; press into an even layer. Bake 11 minutes or until crust puffs and looks dry and set. Place pan on a wire rack.

Mousse: While crust bakes, stir cream, sugar and vanilla in a 1-qt microwave-safe measure or bowl to blend; add chocolate. Microwave on high 2 to 3 minutes until cream barely starts to simmer. Whisk until chocolate melts and mixture is smooth. Cool 8 minutes. Whisk in eggs, 1 at a time, until blended. Pour over hot crust.

Bake 30 to 32 minutes until edges have risen slightly higher than center (middle will be set, but soft).

Glaze: Meanwhile seal semisweet chocolate in a small, sturdy, ziptop bag. Place in a small bowl of hot tap water. Let sit, squeezing bag a few times, until chocolate melts, adding hot water if needed. Melt white chocolate and shortening in a small saucepan over low heat. Stir until smooth.